Express in terms of a new variable

Question

I have a simple expression:

s=4a(x+y)^3

I want to express s in terms of b where b=x+y. That is s will become 4ab^3. How to achieve this in Mathematica?

Eliminate[{s == 4 a (x + y)^3, b == x + y}, {x, y}] or Reduce[{s == 4 a (x + y)^3, b == x + y}, {b, s}, {x, y}] — Artes, Mar 27 '17 at 14:58
Possible duplicate of Can I simplify an expression into form which uses my own definitions? — Daniel Lichtblau, Mar 27 '17 at 18:55

score 2 · Answer 1 · edited Apr 13 '17 at 12:55

2

Already mentioned in the comments(nothing new) by @corey979 and @Artes.

In[49]:= Clear[s, b]

Solve[{s == 4 a (x + y)^3, b == x + y}, s, {x, y}]

Out[50]= {{s -> 4 a b^3}}

edited Apr 13 '17 at 12:55

Community

answered Mar 27 '17 at 17:42

L.K.

1 Answers1